Rotary motor and a method for its manufacture

ABSTRACT

The present invention relates to a rotary motor, preferably a pivot drive for construction machinery, trucks and the like comprising an elongate housing, preferably an approximately tubular housing, a piston displaceably received in the housing, which is axially displaceable by charging with a pressure medium in a pressure chamber, and a shaft received axially fixedly, but rotatably in the housing, with the piston being in screw engagement with the shaft and/or the housing. The invention furthermore relates to a method for the manufacture of such a rotary motor. The present invention departs from the previous approach of separating the sealing of the piston at the shaft and at the housing from the section effecting the rotary guide or the screw engagement. In accordance with the invention, a surface pair of piston and shaft and/or of piston and housing effecting the screw engagement can simultaneously form a sealing surface pair for the sealing of the pressure chamber for the charging of the piston with pressure. The same piston section simultaneously serves the transfer of torque and sealing. A considerably reduced construction length can hereby be achieved since the axial spacing between the sealing section and the rotary guide section or the screw engagement section of the piston is omitted. In addition, the respective components, in particular the housing and the shaft, can be manufactured in an endless manner and be produced as needed and in the required length.

The present invention relates to a rotary motor, preferably a pivotdrive for construction machinery, trucks and the like comprising anelongate housing, preferably an approximately tubular housing, a pistondisplaceably received in the housing, which is axially displaceable bycharging with a pressure medium in a pressure chamber, and a shaftreceived axially fixedly, but rotatably in the housing, with the pistonbeing in screw engagement with the shaft and/or the housing. Theinvention furthermore relates to a method for the manufacture of such arotary motor.

Such a rotary motor is known, for example, from DE 201 07 206 in whichthe piston is guided rotationally fixedly at the inner jacket surface ofthe circularly cylindrical housing, on the one hand, and is in screwengagement on a threaded section of the shaft, on the other hand. If thepiston is axially displaced in the housing by hydraulic charging, itsaxial movement is translated into a rotary movement of the shaft via thescrew engagement. To be able to seal the piston with respect to thehousing and to the shaft and thus to be able to charge the pressurechamber correspondingly with hydraulic pressure, the piston has asealing section which is spaced apart from the screw engagement sectionand which slides on a shaft sealing section, on the one hand, and on thehousing inner jacket surface, on the other hand, and is sealed. Pistonconstructions of this type are, however, disadvantageous with respect tothe construction size and are associated with a high production effort.In addition, different force relationships result for the operation indifferent direction of rotation.

The present invention attempts to provide a remedy here. It has theunderlying object of providing an improved rotary motor of the said kindwhich avoids disadvantages of the prior art and further develops thelatter in an advantageous manner. A rotary motor should in particular beprovided which has a compact construction and is characterized byfavorable torque generation and transfer at the piston.

This object is solved in accordance with the invention by a rotary motorin accordance with claim 1. The named object is solved in a technicalmethod aspect by a method in accordance with claim 21. Preferred aspectsof the invention are the subject of the dependent claims.

The present invention therefore departs from the previous approach ofseparating the sealing of the piston at the shaft and at the housingfrom the section effecting the rotary guide or the screw engagement. Inaccordance with the invention, a surface pair of piston and shaft and/orof piston and housing effecting the screw engagement can simultaneouslyform a sealing surface pair for the sealing of the pressure chamber forthe charging of the piston with pressure. The same piston sectionsimultaneously serves the transfer of torque and sealing. A considerablyreduced construction length can hereby be achieved since the axialspacing between the sealing section and the rotary guide section or thescrew engagement section of the piston is omitted. In addition, therespective components, in particular the housing and the shaft, can bemanufactured in an endless manner and be produced as needed and in therequired length.

The piston advantageously has equally large effective piston surfaces atits two oppositely disposed sides so that no oil store is required assuch. The complete piston surface can effectively be used with equalforces in both directions. The total inner diameter surface of thehousing is practically available on both piston sides as the pistonpressing surface, only reduced by the shaft cross-section. The sametorques can hereby be generated in both drive directions with the samehydraulic pressures. In addition, a maximum torque yield results for agiven pressure.

In a further development of the invention, the screw engagement betweenthe shaft and the piston is not achieved by a conventional threaded meshsection of the shaft and of the piston. The shaft is advantageouslytwisted in itself so that its outer contour forms a spiral polygonalsection twisted around the longitudinal axis of the shaft. This not onlysimplifies the production, but also improves the sealing capabilitybetween the shaft and the piston. The inner jacket surface in screwengagement with the twisted polygonal section can be made free of threadmeshing and have a continuous, constant surface extent withoutimpressions or projections so that the piston and the twisted polygonalsection of the shaft are seated on one another in the manner of a plainbearing surface pair.

To achieve a sealing of the pressure chamber which is as free of leakageas possible, a seal can be inserted into the inner peripheral pistonsurface in screw engagement with the shaft, said seal sealing the pistonon the outer contour of the shaft. The inner peripheral piston surfaceis advantageously likewise made as a polygonal sectional surface whichcan be approximately cylindrical with an axially very short design ofthe piston and in another respect can be slightly twisted in itselfaround the longitudinal axis of the piston, as is the shaft.

Generally, a screw engagement could also be provided between the housingand the piston, in particular in that the housing also forms a polygonalsection spirally twisted around its longitudinal axis. Advantageously,however, the housing has a cylindrical inner jacket surface whichadvantageously has a cross-sectional geometry deviating from thecircular shape at which the piston is longitudinally displaceable guidedand rotationally fixedly supported with its outer jacket surface. Thehousing can in particular have a pressed flat, preferably approximatelyelliptical or oval cross-section. A design of the rotary motor ofshallow construction can hereby be achieved. However, other pressed flatcross-sections can be used which are adapted to the respectiveinstallation situation. In particular when extruded or extrusion moldedsections are used, the outer contour and the inner contour of thehousing can differ from one another in order, on the one hand, to adaptthe outer contour to the installation situation and, on the other hand,to achieve a piston surface which is as large as possible. In accordancewith an embodiment of the invention, the housing can have asubstantially rectangular contour at the outer side. Above all, afavorable torque yield can be achieved with a pressed flat cross-sectionsince a large lever arm is achieved. The housing can advantageously bemade pressed flat such that a longitudinal axis of the cross-section islonger than the transverse axis of the cross-section by at least 30%,preferably by more than 50%.

Generally, different cross-sectional geometries are possible at thehousing. The housing advantageously has a cross-section free of kinksand edges, whereby the sealing capability is improved. In particular anelliptical or oval cross-section combines a good sealing capability witha favorable torque yield. An annularly peripheral seal can be insertedinto the piston outer jacket surface in rotationally fixed engagementwith the inner jacket surface of the housing to achieve a largelyleak-free sealing of the pressure chamber.

The spirally twisted polygonal section of the shaft can likewiseadvantageously have a cross-section pressed flat, e.g. be rectangular orin particular elliptical or oval. To achieve a favorable torque yield,the cross-section can advantageously have a longitudinal axis which isat least 30% and preferably more than 50% longer than the transverseaxis of the cross-section. A square cross-section or a hexagonal sectionwould admittedly also generally be usable in which the ratio oflongitudinal axis to transverse axis of the cross-section substantiallyamounts to 1:1. However, less favorable lever ratios result for thetorque yield there than with a cross-section pressed flat. Thecross-section is advantageously also free of sharp kinks or edges on theshaft to improve the sealing capability.

The favorable torque yield achieved by the pressed flat cross-sectionalprofiles of the housing and/or of the shaft due to lower radial forcesreduces the axial frictional forces acting against the axialdisplacement of the piston, whereby a higher efficiency can be achieved.

In particular with very compact construction dimensions, an optimumtorque yield can take place with a low friction in that the shaft ismade as a winged shaft which has at its periphery at least onerail-shaped projection which is screwed around the shaft axle and viawhich the torques can be borne off ideally. The wing shape can inparticular be made with two wings, i.e. the shaft has two mutuallyopposite radial projections which are each made in rail shape and screwaround the shaft axle. These projections so-to-say form the yield nosesfor the bearing off of torques. In accordance with an advantageousembodiment of the invention, the shaft can have circularly cylindricalsegments between the said projections.

The respective piston seated on the shaft has an inner peripheralsurface which is adapted to the said shaft contour and in whichgroove-shaped recesses are provided which are adapted to the aforesaidwings of the shaft and which engage around the wings and effect thetorque yield between the shaft and the piston.

In order also to achieve an optimum torque yield between the piston andthe housing with very small construction dimensions and with very lowfriction, the piston can also have a wing shape. A winged piston of thistype advantageously likewise has at least one radial rail-shapedprojection which engages into a corresponding groove-shaped recess inthe inner peripheral surface of the housing engaging around it. Inaccordance with a preferred embodiment of the invention, the piston alsohas two mutually opposed wing-like radial projections which engage intocorresponding recesses in the inner peripheral surface of the housing.

With the help of wing shapes of this type at the shaft and/or at thepiston, large load yield levers can be achieved, whereby smallfrictional forces and thus high degrees of efficiency can be achieved.

In accordance with a preferred embodiment of the invention, the housingis made in a compound construction. Such a compound housing can have aplurality of shells which are placed into one another and connected toone another. In this connection, at least one inner shell is expedientlyprovided which is in engagement with the piston and can be adapted toits outer contour and an outer shell is provided which forms the outerskin of the housing. These two shells can be directly connected, inparticular adhesively bonded, to one another with a corresponding designof the outer shell. Alternatively, a support body made of a suitableintegral material, preferably hard foam, aluminum foam or anothersuitable cast mass and/or foam mass, can be provided between the innershell and the outer shell and can connect the inner shell to the outershell. It can not only be achieved in a simple manner by such a compoundconstruction that the outer contour of the outer shell is adapted to theconnecting contours and deviates in cross-section from the inner shelladapted to the piston contour. At the same time, a high stiffness whichbrings along a small gap enlargement at the piston can be achieved bysuch a compound housing with a low weight. With a suitable choice ofmaterial, a high corrosion stability can additionally be achieved, forexample when the outer shell is made of aluminum or of a galvanizedsteel sheet. In addition, the possibility is provided of integratingconnection options, for example to a loading board wall or to a vehicleframe, into the outer shell. On the other hand, the inner runningsurface of the inner shell can be made in a low wear and low frictionmanner. The outer shell and the inner shell can be adapted to differentdemands independently of one another.

The said compound construction of the housing is in particular suitablefor mass production. For a small series production, the housing canalternatively be manufactured in a shaping technology; for example,hydraulic cylindrical tubes can be brought into the desired pressed flatshape by being pressed flat and/or spread while maintaining theirsurface quality.

In accordance with an advantageous embodiment of the invention, thepiston is supported by plain bearings at the housing and/or at theshaft. The plain bearing surfaces at the outer jacket surface and/or atthe inner jacket surface of the piston can simultaneously form thesealing surfaces into which, optionally, separate seals can be inserted.Depending on the design of the rotary motor, a slight leak via the plainbearing surfaces of the piston can be accepted. If this should beavoided, it must be determined in each case that seals can be insertedin a simple manner into the plain bearing surfaces at the outer jacketsurface and/or at the inner jacket surface of the piston. The pistoncan, for example, have hardened jacket surfaces which form the plainbearings. Alternatively or additionally, separate plain bearing insertscan also be provided at the jacket surfaces of the piston. In accordancewith an embodiment of the invention, the piston, in particular itsjacket surface, can also be made of a soft, plasticizing material, withthe housing then being made of a corresponding material to achieve asuitable plain bearing surface pairing.

In accordance with a further preferred embodiment of the invention, thepiston can be supported by roller bearings at the housing and/or at theshaft. A friction further reduced over plain bearings can hereby beachieved. The roller bodies are in this connection arranged at thepiston and roll off at roller body roll-off surfaces at the housingand/or at the shaft. Optionally, roller bearing guide tracks, which arepreferably hardened, can be provided at the housing and/or at the shaft.Advantageously, contour roller bodies are matched whose running surfaceis matched to the contour of the housing or of the running surfaceformed thereon. With an ovally or elliptically curved housing, rollerbodies can thus be used having a running surface correspondingly made inspherical shape in order to achieve a line contact where possiblebetween the roller bodies and the housing.

The twisted polygonal section of the shaft can generally have a pitchremaining constant over the length of the shaft. A translation of theoil feed into a corresponding rotary movement which remains constant ishereby achieved over the total adjustment path of the rotary motor.

In accordance with an alternative embodiment of the invention, thetwisted polygonal section of the shaft can, however, also have a pitchchanging over the length of the shaft. A torque adaptation and arotational speed adaptation of the rotary motor can hereby be achievedwith a constant oil flow, for example a reduction of the rotary speed atthe end of the travel path.

To achieve an increase in the torque with a limited housing diameter, aplurality of pistons can be arranged on the shaft.

In particular, in a further development of the invention, at least twopistons which are to be moved in opposite senses can be arranged on theshaft, with the shaft and/or the housing advantageously havingcounter-revolving screw engagement sections so that the one pistoninteracts with the shaft in a left-handed manner and the other piston ina right-handed manner. An axial force compensation can hereby beachieved in addition to the achieved doubling of the torque. Thebearings of the shaft only have to take up radial forces; the axialforces put onto the shaft by the piston cancel one another.

Alternatively or additionally, a freedom of clearance of the powertraincan also be achieved by two pistons seated on the shaft of the motor.For this purpose, the two pistons are advantageously seated on the sametwisted polygonal section of the shaft and are axially biased withrespect to one another. The axial bias between the two pistons can beeffected mechanically, for example, by a spring and/or hydraulically bypressure charging of the intermediate space between the two pistons.

The shaft can advantageously be supported by means of two bearing coverswhich are seated axially at the end face on the oppositely disposed endsof the housing. Seals can in each case be provided between the bearingcovers and the shaft for the sealing of the pressure chamber. The sealsare advantageously integrated into the respective bearing surface atwhich the shaft is supported at the bearing cover.

The support of the shaft at the bearing cover can advantageously be aplain bearing. Alternatively or additionally, a roller bearing withroller bodies can also be provided here between the respective bearingcover and the shaft.

The shaft advantageously passes through the bearing cover at both sides.The shaft stubs projecting at the respective housing head can form theoutput elements via which the torque is output.

The polygonal section of the shaft deviating from the circular shape incross-section can advantageously be used directly to achieve the torqueyield. Alternatively, a connector piece can, however, be rotationallyfixedly fastened to the shaft ends, for example welded on or pressed on.

The polygonal section twisted in itself can be put on the shift indifferent manners. Optionally, one could think of working the polygonalsection in a cutting process. In accordance with an advantageous aspectof the present invention, the polygonal section twisted in itself is,however, manufactured by non-cutting shaping. The shaft can be shapedfrom a substantially cylindrical shaft blank which has a polygonalsectional cross-section differing from the circular shape. This shaftblank can be cut to the desired length from an endless bar section. Theshaft blank is twisted itself around its longitudinal axis bynon-cutting shaping so that its outer contour forms the polygonalsection twisted in itself effecting the screw engagement with thepiston. The shaping can take place by cold twisting or hot twisting. Itwill be appreciated that the manufacture of the shaft does not have totake place in a completely non-cutting manner. Optionally, the surfaceof the shaft can be worked in a cutting manner, in particular polished,before or after the twisting. Optionally, the shaft blank can also begiven its polygonal section by cutting processing. The twisting of thepolygonal section, however, advantageously takes place in a non-cuttingmanner.

If the shaft should cooperate in the previously described manner withtwo pistons working in opposite senses, the shaft blank isadvantageously twisted starting from a direction change section towardoppositely disposed sides in a counter-revolving manner. The shaftmanufactured in this manner is shaped from an integrally one-piece shaftblank.

Alternatively, two shaft blanks twisted in opposite senses can berigidly connected to one another, in particular welded and/or screwed toone another, so that the shaft hereby created has two shaft sectionstwisted in opposite senses.

The invention will be explained in more detail in the following withreference to preferred embodiments and to associated drawings. There areshown in the drawings:

FIG. 1: a longitudinal section through a rotary motor in accordance withan advantageous embodiment of the invention in which two pistons workingin opposite senses to one another are arranged on the shaft twisted inopposite senses;

FIG. 2: a cross-section through the rotary motor of FIG. 1 which shows apiston supported by plain bearings on the oval housing and on the shaft;

FIG. 3: an end-face plan view of the housing motor of FIG. 1 which showsa bearing cover screwed to the housing and a fastening lever integratedin the bearing cover as well as the shaft of the motor going beyond thebearing position with a bearing ring;

FIG. 4: a cross-section through the rotary motor of FIG. 1 which showsthe floating support of the shaft at its direction change sectionlocated at the center;

FIG. 5: a cross-section through the rotary motor of FIG. 1 in the regionof an end-face bearing cover with a throughgoing shaft and a shaft stubturned on;

FIG. 6: a sectional cross-section in the region of a bearing cover inaccordance with a further embodiment of the invention with a bearingstub welded to the shaft;

FIG. 7: a sectional cross-section in the region of a bearing cover inaccordance with a further embodiment of the invention in which thetwisted shaft goes through the bearing cover;

FIG. 8: a cross-section through the rotary motor of FIG. 1 which shows apiston outer support at the oval housing with inserted plain bearings;

FIG. 9: the plain bearing support of the piston at the housing of FIG. 8in a longitudinal section;

FIG. 10: a cross-section through the rotary motor which shows a supportof the piston at the oval housing by means of roller bearings;

FIG. 11: the roller bearing support of the piston at the housing of FIG.10 in a longitudinal section;

FIG. 12: a roller bearing support of the piston at the housing in alongitudinal section similar to FIG. 11, with, in accordance with analternative embodiment of the invention, a plurality of roller bodiesbeing provided spaced apart from one another axially;

FIG. 13: a longitudinal section through a piston of the rotary motorwith pressure-charged, valve-controlled inner lubrication;

FIG. 14: a longitudinal section through a rotary motor in accordancewith a further embodiment of the invention in which two mutually biasedpistons effect a freedom of clearance of the powertrain, with the biastaking place by a spring and by a pressure fluid charging;

FIG. 15: a longitudinal section through a rotary motor with two biasedpistons similar to FIG. 14, with the two pistons only being biasedmechanically by springs in this embodiment;

FIG. 16: a cross-section through the rotary motor which shows thesupport of the piston at the shaft by means of roller bearings;

FIG. 17: the roller bearing support of the piston at the shaft of FIG.16 in a longitudinal section which permits pitch changes at the shaft;

FIG. 18: a roller bearing support of the piston at the shaft in alongitudinal section similar to FIG. 17, with roller bodies beingprovided spaced apart axially from one another in the embodiment of FIG.18;

FIG. 19: a cross-section through the rotary motor in accordance with analternative embodiment of the invention which shows a spherical guidanceof the piston at the shaft which permits changes of pitch of the shaft;

FIG. 20: a side view of the spherical support of the piston at the shaftof FIG. 19 in a longitudinal section;

FIG. 21: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows an alternative rollerbearing support of the piston at the flat sides of the shaft;

FIG. 22: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows an alternative rollerbearing support of the piston at the flat side of the shaft;

FIG. 23: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows a plain bearing supportof the piston at the shaft with inserted guide pieces;

FIG. 24: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows an alternative plainbearing support of the piston at the flat sides of the shaft, withhardened round wire sections inserted into the shaft being provided;

FIG. 25: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows a four-point rollerbearing support of the piston at the shaft with a peripheral roller bodytrack;

FIG. 26: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which shows a two-point rollerbearing support of the piston at the flat sides of the shaft with a ballreturn;

FIG. 27: the roller bearing support of the piston at the shaft with aball return from the preceding Figures in a longitudinal section;

FIG. 28: a sectional cross-section in the region of a bearing coverwhich shows the screw connection of the bearing cover to the tubularhousing;

FIG. 29: a sectional cross-section in the region of the bearing cover inaccordance with a further embodiment of the invention which shows a weldconnection of the bearing cover to the tubular housing;

FIG. 30: a sectional cross-section in the region of a bearing cover inaccordance with a further embodiment of the invention which is securedto the tubular housing by securing rings inserted radially into thehousing cover;

FIG. 31: a longitudinal section through a continuously produced shaftwith direction change;

FIG. 32: a sectional longitudinal section through a shaft which has adirection change and is composed of two shaft pieces which areelastically coupled to one another;

FIG. 33: a sectional longitudinal section through a shaft in accordancewith a further embodiment of the invention which consists of two shaftsections of opposite senses which are friction welded to one another;

FIG. 34: a sectional longitudinal section through a shaft with directionchange which is composed of two shaft pieces which are screwed to oneanother;

FIG. 35: a cross-section through the rotary motor in accordance with afurther embodiment of the invention in which the housing consists of anextruded or extrusion molded section whose outer contour differs fromits inner contour in order, on the one hand, to adapt the outer contourto the installation situation and to achieve a piston surface which isas large as possible in the inner space;

FIG. 36: a cross-section through the rotary motor of FIG. 34 which showsthe support of the shaft at its direction change section located at thecenter; and

FIG. 37: a cross-section through the rotary motor in accordance with afurther embodiment of the invention which is made as a wing motor inwhich the shaft and the piston each have a wing shape in order toachieve an optimum torque yield with low friction with very compactconstructional dimensions;

FIG. 38: a cross-section through the rotary motor in accordance with afurther embodiment of the invention, according to which the shaft, thepiston and the housing each have pressed-flat, oval or ellipticalcross-sections and the housing can consist of a pressed-flat or spreadcylindrical tube, with an excellent torque yield being able to beachieved with low friction by the pressed-flat cross-section andlikewise with a very compact constructional dimension;

FIG. 39: a representation of the winged shaft of the torque embodimentof FIG. 37, the shaft being made as a hollow shaft and being shown incross-section in accordance with a) and in a side view in accordancewith b);

FIG. 40: a cross-sectional representation of the housing of the rotarymotor made as a wing motor of FIG. 37, with the house being made incompound construction and having an elliptical outer shell as well as aninner shell adapted to the wing contour of the piston which areconnected to one another to form a support body of integral material;

FIG. 41: a cross-sectional representation of the housing of the wingmotor of FIG. 37 in compound construction in accordance with analternative embodiment of the invention in which the outer shell isadapted to the connection geometry of the component to be connected andhas integrated securing means; and

FIG. 42: a cross-sectional representation of the housing of the wingmotor of FIG. 37 in compound construction in accordance with a furtheralternative embodiment of the invention in which the outer shell of thehousing is made as an extruded section or as an extrusion molded sectionand is seated on the inner shell with a gap-filling material.

The rotary motor 1 shown in FIG. 1 includes a cylindrical tubularhousing 2 which is made of an endless bar material and was cut to thedesired length. A shaft 3 is arranged in the housing 2 coaxially to itslongitudinal axis and is supported rotatably, but axially fixedly, totwo bearing covers 4 closing the housing 2 at the end face. In theembodiment drawn, the shaft 3 is additionally supported centrally at thehousing 2 by a floating shaft bearing support 5 to prevent any saggingof the shaft 3.

The shaft 3 advantageously has a pressed-flat cross-section as is shown,for example, by FIG. 2. The longitudinal axis 6 of the cross-section ismore than twice as long as the transverse axis 7 of the cross-section inthe embodiment drawn in accordance with FIG. 2. Overall, thecross-section of the shaft 3 forms a pressed-flat polygonal sectiondeviating from the circular shape and having two flat sides 8 which areparallel to one another and are chamfered in each case towards thenarrow side 9 so that the cross-sectional profile is free of kinks andedges overall (cf. FIG. 2).

As FIG. 1 shows, the polygonal section of the shaft 3 is spirallytwisted in itself, with the shaft 3 having a direction change at itscenter. From the central direction change section, the shaft 3 istwisted in itself in different direction towards its two ends so thatone shaft half is made in a left handed manner and the other shaft halfis made in a right handed manner.

Two pistons 10 are seated on the shaft 3 which act in opposite sensesand which are each seated in a precise fit on the polygonal section ofthe shaft 3 so that they are in screw engagement with it. On the otherhand, the pistons 10 are guided axially displaceably, but rotationallyfixedly in the housing 2 so that an axial movement of the pistons 10 istranslated into a rotary movement of the shaft 3 relative to the housing2.

As FIG. 2 shows, the rotationally fixed guidance of the pistons 10 inthe housing 2 is effected in that the housing 2 has a cross-sectiondiffering from the circular shape. As FIG. 2 shows, it can in particularhave a pressed-flat, substantially oval or elliptical cross-sectionwhich substantially corresponds to the outer cross-section of the piston10.

The pistons 10 can be axially driven by being charged with a pressuremedium, which can generally be air or another gas, but advantageously aliquid, in particular hydraulic oil, so that the shaft 3 carries out thedesired rotary movement. For this purpose, the pistons 10 can be sealedboth with respect to the shaft 3 and to the housing 2. As FIG. 1 shows,a shaft seal 12, which seals the respective piston 10 with respect tothe shaft 3, is seated in the inner jacket surface 11 of the pistons 10.A housing seal 14, which seals the respective piston 10 with respect tothe housing 2, is in each case seated on the outer jacket surface 13 ofthe pistons 10. Accordingly, a pressure chamber 15, 16, 17 and 18 isprovided on each side of the pistons 10 and is bounded, in addition tothe respective piston surface, by the housing 2 and, in the case of thepressure chambers 15 and 18, by the housing cover 4. The pressurechambers 15, 16, 17 and 18 can be filled with pressure fluid in a mannerknown per se to move the pistons 10 to and fro. The pressure feed system19 advantageously includes pressure fluid feed passages 20 which extendon the interior of the shaft 3. They can be in communication withpressure fluid feed passages 21 which extend on the interior of thepivot levers 29 which are seated rotationally fixedly on the shaft stubs23 which exit the housing 2 through the bearing covers 4.

In the embodiment shown in FIG. 2, the pistons 10 are each supported bya plain bearing with respect to the housing 2 and the shaft 3, i.e. theouter jacket surface and the inner jacket surface 10 each form plainbearing surfaces.

As FIG. 3 shows, the bearing covers 4 closing the housing 2 at the endface are screwed to the housing 2. Fastening levers 24 or abutments canadvantageously be integrated into the bearing covers 4 to intercepttorques introduced from the housing 2. As FIGS. 1 and 3 show, the shaft3 is in each case supported in the bearing covers 4 by a bearing ring 25which is fixedly connected to the shaft 3 and is rotatably supported inthe bearing cover 4. Both axial forces and radial forces can beintercepted via the bearing rings 25, although axial forces arecompensated per se by the dual-piston arrangement and thus substantiallyonly radial forces act on the shaft.

FIG. 4 shows the floating shaft support 5 supporting the shaft 3centrally in greater detail. An intermediate support ring 26 is fixedlyseated on the direction change section of the shaft 3 and is supportedin a floating manner in a guide plate 27 which has a cylindrical orslightly spherically arched inner recess in which the intermediatesupport ring 26 is received. The guide plate 27 is adapted at its outerperiphery to the oval or elliptical housing section and is supported atthe housing 2.

The take-up of the torque from the shaft 3 can generally take place indifferent manners. As FIG. 5 shows, the shaft 3 can have, at its two endface ends, two shaft stubs 13 which are turned on and which pass throughthe respective bearing covers 4 and advantageously respectively have aflattened section 28 onto which the respective pivot levers 29 can beplaced. In this embodiment, the shaft stub 13 is therefore madeintegrally from material of the shaft 3. The polygonal profile sectionfor the screw engagement with the respective piston 10, however, onlyextends inside the housing up to the bearing covers 4 (cf. FIG. 5).

Alternatively, the shaft stub 13 can also, as FIG. 6 shows, first bemade as a separate component and be set onto the shaft 3 and be rigidlyand rotationally fixedly connected thereto. This has the advantage thatthe diameter of the shaft stub 13 is not restricted by the geometry ofthe polygonal section of the shaft 3. The shaft stub in accordance withFIG. 6 can in particular be welded to the shaft 3, with a flattenedsection 28 also being provided here.

Alternatively, the twisted polygonal section of the shaft 3 can itselfbe guided through the bearing cover 4 and be supported on it. For thispurpose, a support ring 30 is seated on the polygonal section of theshaft 3 and is rotatably supported, but axially fixedly supported, inthe respective bearing cover 4, as FIG. 7 shows. The support ring 20can, for example, be welded to the shaft 3. In any case, the shaft 3 issupported axially fixedly, but rotatably.

The outer support of the pistons 10 at the inner periphery of thehousing 2 can generally take place in different manners. Instead of theplain bearing support shown in FIG. 2 in which the plain bearing surfaceof the piston is formed from its actual material, provision can also bemade in accordance with FIG. 8 that corresponding plain bearing stones31 of special plain bearing material are inserted into the outerperipheral surface of the respective piston 10. These plain bearingstones 31 are advantageously offset away from the center towards theflat sides of the piston to achieve a lever arm which is as large aspossible on the torque support at the housing 2, as FIG. 8 shows. In theembodiment drawn in FIG. 8, the plain bearing stones 31 lie in the outerthird of the piston 10 with respect to the cross-sectional longitudinalaxis of the piston 10. The support stones 31 can be aligned in the ballcup-like recesses in the piston 10 by the circular contour andaccordingly adapt to the contour of the housing or to the load yield.

As FIG. 9 shows, the plain bearing stones 31 are advantageously offsetin the axial direction of the piston 10 towards its pressure chargingsides and are arranged pair-wise on oppositely disposed sides of thehousing seal 14. The arrangement of the housing seal 14 centrallybetween the plain bearing stones 31 ensures their lubrication sincepressure medium can moved from the respective pressure chamber betweenthe piston outer jacket surface 13 and the housing inner jacket surfaceuntil it impacts the seal 14.

Alternatively to the described plain bearing support, the respectivepiston 10 can also be supported by a roller bearing support 32 at thehousing 2. As FIGS. 10 and 11 show, the roller bodies 33 can be arrangedcentrally with respect to the longitudinal direction of the piston 10and, viewed in cross-section in accordance with FIG. 10, can be movedoutwardly towards the narrow side of the piston 10 in the direction ofthe cross-sectional longitudinal axis to achieve a good lever arm forthe torque interception. Generally, at least two roller bodies 33,advantageously, however, at least four roller bodies 33, are provided,with the roller bodies optionally also being able to be madeelastically. As FIG. 11 shows, housing seals can be provided at thepiston 10 at the outer jacket surface 13 of the respective piston 10 tothe right and to the left of the roller bearing support 32.

As FIG. 12 shows, the roller bearing support 32 can advantageously alsocomprise a plurality of roller boy pairs 33 which, viewed in the axialdirection of the piston 10, are arranged sequentially and moved towardsthe two pressure charging surfaces of the respective piston 10. Tiltmovements of the piston 10 can thereby be better intercepted to acertain degree. In addition, a central seal 14 can be used at the outerjacket surface 13 of the piston 10 for its sealing with respect to thehousing 2 and, as FIG. 12 shows, is arranged between the roller bodies33 viewed in the axial direction. Pressure medium can hereby penetratebetween the piston outer jacket surface 13 and the inner jacket surfaceof the housing 2 and thereby lubricate the roller bodies 13.

Irrespective of whether the piston is supported by plain bearing orroller bearing, an inner lubrication of the bearing positions can alsobe provided, as FIG. 13 shows. For this purpose, a pressure passagesystem 34 can be formed in the respective piston 10 and canadvantageously have a pressure storing property or an actual pressurestore 53, with the pressure passage system 34 being connected via a feedbore 35 to the bearing position of the piston 10 at the housing 2 and/orvia a feed bore 36 to the bearing position of the piston 10 at the shaft3 to provide lubricant thereto.

The pressure passage system 34 can advantageously be fed by the pressurechambers for the actuation of the piston 10, as FIG. 13 shows. Thepressure passage system 34 in the interior of the piston 10 cancommunicate via feed bores 37 and check valves 38 with the end faces ofthe piston 10 in order to be supplied with pressure fluid on pressurecharging of the respective chamber. As FIG. 13 shows, seals 12 and 14can be provided at both sides of the support positions on the internallubrication of the support positions of the piston 10.

In a similar manner as the internal lubrication, a bias of the pistons10 or of the guide elements 41 or 42 on the shaft 3 and thus a freedomof clearance can also be achieved, as FIG. 14 shows. For this purpose,each piston 10 comprises two piston parts 10 a and 10 b which areaxially displaceable with respect to one another, but are guidedrotationally fixedly at the housing 2 and are in screw engagement withthe shaft 3. The two piston parts are axially biased with respect to oneanother via a spring device 39 which can be a compression spring in theembodiment drawn in FIG. 14. Alternatively or additionally to the springdevice 39, a bias of the two piston parts 10 a and 10 b canadvantageously also take place by the pressure medium.

As FIG. 14 shows, the intermediate space 40 between the two piston parts10a and 10 b communicates via check valves 38 with the respectivelypressure charged side of the piston 10 which is the right hand side inFIG. 14. The pressure fluid enters into the intermediate space 40 viathe check valves 38 at the pressure P so that the pressure P is alsopresent therein. It is thereby ensured that the pressure P is borne offvia the piston part at the front in the direction of movement, that isthe piston part 10 a in accordance with FIG. 14. The rear piston part 10b follows without pressure, since the same pressure P is applied at bothsides. It is ensured via the compression spring 39 that the piston partat the front in the direction of movement, which bears off the pressure,or the piston guide provided thereat, contacts the respectivelyforwardly disposed screw thread flank so that clearance is precluded.

FIG. 15 shows a similar piston design 10 with bias and thus freedom ofclearance. In contrast to FIG. 14, the pressure P is, however, borne offvia the respective rear piston part, with the spring device 39consisting of tension springs in this connection attempting to pull thetwo piston parts 10 a and 10 b or the guide elements toward one anotherso that they are in screw engagement with the shaft 3 without clearance.It is understood that both piston parts 10 a and 10 b are alsorotationally fixedly guided at the housing 2 and are in screw engagementwith the shaft 3 in the embodiment in accordance with FIG. 15.

To reduce the friction of the piston, it can be supported not only atits outer side by a roller bearing support at the housing 2; the piston10 can instead also have a roller bearing support 41 instead of a plainbearing support at the shaft 3. In the embodiment drawn in the FIGS. 16and 17, the shaft 3 can have a substantially rectangular cross-section,with the inner roller bearing support 41 of the piston 10 having rollerbodies 42 which are seated at the edge of the flat sides of the shaftsection, as FIG. 16 shows. The roller bodies 42 can optionally havemarginal webs via which they are guided at the narrow sides of thepolygonal section of the shaft 3. As FIG. 17 shows, the roller bodies 42can be arranged centrally at the inner jacket surface 11 of the piston10 viewed in the longitudinal direction. Shaft seals 12 can be arrangedat both sides of the inner roller bearing support 41 at the inner jacketsurface 11 of the piston 10.

Alternatively, a plurality of roller body pairs 42 can also be arrangedspaced apart from one another at the inner periphery of the piston 10 inthe axial direction with the roller bearing support 41, as FIG. 18shows. Tilting torques acting on the piston 10 can be intercepted betterto a certain degree by the arrangement of the roller bodies with respectto the pressure charged end faces of the piston 10. In addition, asealing 12 arranged between the roller bodies 42 is sufficient so thatan external lubrication of the bearing positions is simultaneouslypossible since, on pressure charging from one side, pressure medium canmove between the shaft 3 and the inner jacket surface 11 of the piston10.

The previously described arrangement of the inner roller bearing support41 with only centrally arranged roller bodies 42 in accordance with FIG.17, in contrast, has the advantage that pitch changes or pitch defectsof the twisted polygonal section of the shaft 3 are possible.

To permit, on the one hand, a compensation of pitch changes or pitchdefects in the twisted polygonal section of the shaft 3, but, on theother hand, nevertheless to ensure a load removal over a larger area,the pistons 10 can also be supported in each case by spherical guideelements 43 at the flanks of the shaft 3. The spherical guide elements43 are inserted in ball cups in the inner peripheral surface 11 of thepistons 10 so that they twist in a multiaxially manner and can thusadapt to pitch changes. In the embodiment drawn in FIG. 19, thespherical guide elements 43 can form gliding stones which slidinglysupport the piston 10 at the shaft 3. It is, however, generallyconceivable that roller bodies are fastened to the spherical guideelements 43 to achieve a roller bearing support.

A roller bearing support of the pistons 10 at the shaft 3 does not haveto be restricted to an arrangement of the roller bodies at the flatsides 2 of the shaft 3. As FIG. 21 shows, the inner roller bearingsupport 41 of the pistons 10 can also comprise roller bodies 42 whichrun on the narrow sides 9 of the polygonal section of the shaft 3. Inthe embodiment drawn in FIG. 21, concave running tracks for thespherical roller bodies 42 are introduced into the narrow side 9 of theshaft 3 so that they also guide transversely to their running direction.

FIG. 22 shows an alternative to this. The narrow sides 9 of the shaft 3can naturally also form spherical guide running tracks for the rollerbodies 42 which have a convexly arched running surface in thisembodiment (cf. FIG. 22). A transverse guidance of the roller bodies 42with respect to the shaft 3 can also thereby be achieved.

With a plain bearing support of the pistons 10 on the shaft 3, thecorresponding plain bearing surfaces can generally be formed by thematerial of the pistons 10. Optionally, for this purpose, the innerjacket surface of the pistons 10 can be hardened and/or worked in asuitable manner. Sliding stones 44 of a suitable plain bearing materialcan, however, advantageously be inserted into the inner jacket surface11 of the pistons 10, as FIG. 23 shows. In this embodiment, the shaft 3has a substantially rectangular cross-section with side flanks 45chamfered toward the rim. The sliding stones 44 which are inserted intothe inner jacket surface 11 of the piston 10 and whose rear side can becircular to achieve a self-adjustment run on these inclined side flanks45.

As FIG. 24 shows, the sliding stones 44 can also be provided on thenarrow sides 9 of the polygonal section of the shaft 3. The slidingstones 44 can advantageously have a spherical sliding surface which isset into a concave sliding surface in the narrow side 9 of the shaft 3,as FIG. 24 shows. A transverse guidance is hereby achieved. The slidingstones 44 can in particular be made of hardened round wire sectionswhich are inserted into the shaft 9 and on which the narrow sides of thepiston 3 run in the manner drawn in FIG. 24.

With a roller bearing support of the pistons 10 on the shaft 3, theroller bodies 42 can generally be guided in a roller body cage formed inaccordance with the shaft body extent. Alternatively, however, an innerroller arrangement 41 can also be provided with peripheral roller bodies42 and a return of the roller body 42, as FIG. 25 shows. In thisconnection, a roller body return passage 46 can be provided in therespective pistons 10 and the roller bodies 42 can be returned by itfrom the end of the roller body track between the piston and the shaft 3to the start of the said roller body track. A constant circulation ofthe roller bodies 42 results, as indicated by the arrow 47 in FIG. 25.

Such a roller body return is naturally possible both with four-pointroller bearing supports, as FIG. 25 shows, and with two-point rollerbearing supports, as FIG. 26 shows, and also irrespective of whether theroller bodies 42 run on the flat sides 8 of the shaft 3 or on the narrowsides 9 of the shaft 3, as FIG. 26 shows. FIG. 27 illustrates the returnof the roller bodies 42 via the roller body return passage 46. Thereturn is in particular also advantageously made in the embodiment shownin FIG. 25 such that a raising of the balls is ensured and such thatthey can be returned with clearance, so-to-say free of force.

There are different possibilities with respect to the fastening of thebearing covers 4 to the housing 2. In addition to the screw connectionof the bearing covers 4 to the end faces of the housing 2 shown in FIG.28, the bearing covers 4 can also be welded to the housing 2, as FIG. 29shows. Alternatively to this, the bearing covers 4 can also be insertedinto the cylindrical housing 2 and can be secured to its inner jacketsurface by securing rings 48 (cf. FIG. 30).

There are also generally different possibilities with respect to theproduction of the shaft 3. In accordance with an advantageous embodimentof the invention, the shaft 3 can be made of one piece, and indeed alsowhen it has a direction change and has at least one right hand sectionand at least one left hand section, as FIG. 31 shows. For this purpose,starting from a direction change section 49, the initially cylindricalshaft blank which differs from the circular shape in cross-section canbe twisted in opposite senses toward its ends, for example by coldshaping or hot shaping, so that the right hand and left hand screwengagement sections 50 a and 50 b shown in accordance with FIG. 31 arecreated. Toward the end, the twisting-in-itself of the shaft section canbe stopped to obtain non-twisted shaft stubs 23 which facilitate theconnection of corresponding pivot levers for the torque pick-up. Thepreviously described bearing rings 20 can be welded onto the integrallyproduced shaft 3 to be able to support the shaft 3 in the bearing covers4.

Alternatively, the double-threaded shaft 3 can be made from two pieces,as FIGS. 32 to 34 illustrate. Two shaft pieces twisted in themselves canbe screwed together at the end face, preferably via two coupling pieces51, which are fixedly seated on the shaft pieces and are made elastic orcan effect an elastic coupling (cf. FIG. 32).

Alternatively, the two shaft pieces of the shaft 3 can also be connectedto one another in a firmly bonded manner, in particular by frictionwelding 52 (cf. FIG. 33).

As FIG. 34 shows, a screw connection or a butt joint of the right handand left hand shaft pieces is also possible. For this purpose, the twoshaft pieces can be inserted into a screw connection sleeve in whichthey are fixed by a transverse screw connection.

In the embodiment shown in FIGS. 35 and 36, the housing 2 is extruded ormade as an extrusion molded section. A housing can thereby in particularbe manufactured whose outer contour differs from its inner contour. Theouter contour, which is made substantially rectangular in accordancewith FIGS. 35 and 36, can be adapted to the respective installationsituation. At the same time, with the outer contour preset by theinstallation situation, the inner contour of the housing 2 can be madesuch that a useful piston surface is achieved which is as large aspossible. As FIG. 35 shows, the housing section has a plurality of axialbores in which tie bars or screw bolts are received in order, forexample, to fasten the end-face covers. The inner contour of the housing2 fits snugly around these axial bores and, in another respect, followsthe outer contour—predetermined by the required wall thickness—toachieve a piston cross-sectional surface which is as large as possible.

The central shaft bearing support 5, which supports the shaft 3centrally at its direction change section, can advantageously also befastened to the threaded bars. The central shaft bearing support 5 canadvantageously also be made as an axial bearing in order, for example,to be able to take up residual axial forces resulting from pitch defectsof the shaft. Advantages can be achieved with respect to the kink lengthof the housing 2 and/or of the shaft 3 by a central axial bearingsupport of the shaft 3.

In another respect, FIG. 36 shows two passage bores 50 in the guideplate 27 and the pressure chambers 16 and 17 can be connected with oneanother through them.

In the embodiment shown in FIG. 37, the shaft 3 and the piston 10 eachhave a wing shape. As in particular FIG. 39 shows, the shaft 3 comprisesa cylindrical, in particular a circularly cylindrical, base body 63 onwhose outer jacket surface yield noses 60 are provided in the form ofrail-like wing projections 64 which are arranged disposed oppositely oneanother and are wound around the axis of rotation of the shaft 3. Thewinged shaft formed in this manner can advantageously be manufactured bymilling. The said rail-like wing projections 64 extend spirally and canadvantageously be shaped integrally in one piece at the base body 63.The maximum shaft diameter measured in the region of the oppositelydisposed wing projections 64 is, in the embodiment drawn, approximately30 to 40% larger than the minimum shaft diameter measured in the regionof the base body 63, cf. FIG. 37. The base body 63 advantageously has afairly large diameter with a circularly cylindrical design to achieve agood torque yield, with the radial overhang of the wing projections 64being dimensioned only so large that the permitted surface pressing isobserved with the torque yield. The volume to be displaced can alsothereby be kept small. The shaft 3 can in particular be designed as atorsion shaft with a large pitch.

As FIGS. 37 and 39 show, the shaft 3 is made as a hollow shaft. Thisdoes not only effect a reduction in weight. At the same time, the axialcut-out 61 at the interior of the shaft 3 can be used as a bore for theoil feed.

The piston 10 is adapted at its inner peripheral surface to the outercontour of the shaft 3. The piston 10 in particular has a circularlycylindrical inner cut-out in the embodiment drawn in accordance withFIG. 37 which has groove-shaped recesses at oppositely disposed sideswhich engage around the said wing projections 64 in a shape-matchedmanner, cf. FIG. 37.

At its outer contour, the piston 10 likewise has two yield noses 62 inthe form of rail-shaped radial wing projections 65 on oppositelydisposed sides, cf. FIG. 37. The outer contour of the piston 10 isbounded by a segmentally circularly cylindrical and/or ellipticalperipheral surface between the said wing projections 65.

The inner peripheral surface of the housing 2 is adapted in acorresponding manner to the wing shape of the piston 10.

Alternatively, the rotary motor can also have the pressed-flatcross-sections, in particular elliptical or oval cross-sections, shownin FIG. 38. As FIG. 38 shows, the shaft 3 can also be made as a hollowshaft in this embodiment, whereby the inner axial cut-out 61 can be usedas a bore for the oil guide. The shaft 3 is twisted in itself in thisconnection in its oval or elliptical cross-section, i.e. around its axisof rotation, so that it forms an oval or elliptical spiral shaftoverall. The shaft 3 can in particular be cast and ground. The shaft 3can optionally also be swirled; however, a better surface quality isimmediately achieved by grinding.

The housing 2 can consist in the embodiment drawn in FIG. 38 of acylindrical tube which can be pressed or spread into the desired flatshape while maintaining its surface property.

A smaller load yield lever is created by the oval or elliptical shapeshown in FIG. 38 than in the embodiment drawn in FIG. 37; however, thissmaller load yield lever is easy to compensate due to the specific formdrawn.

The housings 2 are each shown with one shell in FIGS. 37 and 38. In bothembodiments, in particular, however, in the embodiment of FIG. 37, thehousing 2 can be made in compound construction. An embodiment of such acompound construction of the housing is shown in FIG. 40, according towhich the inner shell 66 adapted to the wing shape of the piston 1 issurrounded by a support body 67 which is in turn enveloped by an outershell 68. The different shells advantageously consist of differentmaterials and are adapted to their respective function. The inner shell66 can, for example, consist of a suitable metal and preferably have ahardened, for example a nitrated, inner surface to form a low-wear andlow-friction running track for the piston 10. The support body 67advantageously consists of a suitable integral material and can inparticular be made from hard foam, aluminum foam or a suitable castingmass. The elliptical outer shell 68 in the drawn embodiment inaccordance with FIG. 40 can consist of different materials. Anadvantageous embodiment can consist of the fact that the outer shell 68consists of fiber-reinforced plastic, for example a GRP reinforcedwrapping material.

A sandwich-like structure of the housing 2 with an inner shell and anouter shell of hard-surface, high-strength material and a support bodyconnecting them of a lighter, less impact-resistant material can achievevery high strengths and shape stabilities with a low weight and canmoreover effect the advantages first mentioned.

As FIG. 41 shows, the outer shell 68 can also be adapted to theconnection geometry of a component to be connected to the housing 2. Theouter shell 68 can in particular have at least one plane contact surface69. It is advantageously possible to give the outer shell 68 asubstantially cubic shape overall. Alternatively or additionally,fastening options can be integrated into the housing 2 in a simplemanner by the compound construction. As FIG. 41 shows, threaded nuts 70can, for example, be set onto the outer shell 68 from the inner side andbe foamed into the housing 2.

Alternatively to a three-shell structure of the housing 2 with a supportfoam body, the inner shell 66 can also be directly embedded into theouter shell 68, as FIG. 42 shows. The outer shell 68 is in thisconnection advantageously made as an extrusion section or as anextrusion molded section. The outer shell 68 can, for example, beextruded from GRP or pressed from an aluminum extrusion. The outer shell68 advantageously comprises a plurality of axial hollow spaces 72, witha uniform cross-section being provided overall in the axial direction.Securing options, for example in the form of threaded nut receivers 71,can also be integrated into the shell in the embodiment in accordancewith FIG. 42.

1. A rotary motor, preferably a pivot drive for construction machinery,trucks and the like, comprising an elongate housing (2), preferably anapproximately tubular housing, at least one piston (10) displaceablyreceived in the housing (2), which is axially displaceable by chargingwith a pressure medium in a pressure chamber (15, 16, 17, 18), and ashaft (3) received axially fixedly, but rotatably in the housing (2),with the piston (10) being in screw engagement with the shaft (3) and/orthe housing (2), wherein a surface pair (8, 9; 11) of piston (10) andshaft (3) and/or of piston (10) and housing (2) effecting the screwengagement simultaneously forms a sealing surface pair for the sealingof the pressure chamber (15, 16, 17, 18) for the pressure charging ofthe piston (10).
 2. A rotary motor in accordance with claim 1, whereinthe piston (10) has equally large effective piston surfaces on its twooppositely disposed sides for the pressure charging by the pressurechambers (15, 16, 17, 18).
 3. A rotary motor in accordance with claim 1,wherein the shaft (3) has a polygonal sectional cross-section differingfrom the circular shape in at least one screw engagement section (50)and is twisted spirally around its longitudinal axis.
 4. A rotary motorin accordance with claim 1, wherein the shaft (3) is made as wingedshaft whose cross-section has at least one radially projecting wing-likeyield nose (60), preferably two mutually oppositely disposed such yieldnoses (60), for the torque yield.
 5. A rotary motor in accordance withclaim 1, wherein the shaft (3) has a circular cross-section, apart fromthe at least one yield nose (60), viewed in cross-section.
 6. A rotarymotor in accordance with claim 1, wherein the outer diameter of theshaft (3) is larger in the region of the at least one yield nose (60) byat least 15%, preferably by approximately 25 to 50%, than the outerdiameter of the shaft (3) in sections without a yield nose.
 7. A rotarymotor in accordance with claim 1, wherein the shaft (3) has asubstantially oval cross-section.
 8. A rotary motor in accordance withclaim 1, wherein the shaft (3) is made as a hollow shaft and/or has anaxial cut-out (61) in its interior for the supply and/or draining of thepressure medium.
 9. A rotary motor in accordance with claim 1, wherein aseal (12) is inserted into the inner jacket surface (11) of the piston(10) being in screw engagement with the shaft (3).
 10. A rotary motor inaccordance with claim 1, wherein the piston (10) has an inner cut-outwhich forms a profile section substantially corresponding to thecross-section of the shaft (3).
 11. A rotary motor in accordance withclaim 1, wherein the piston (10) is made as a wing piston whosecross-section at the outer periphery has at least one radiallyprojecting yield nose (62), preferably two mutually oppositely disposedsuch yield noses (62), for the torque yield with respect to the housing(2).
 12. A rotary motor in accordance with claim 11, wherein the piston(10) has a contour corresponding to the flat side of an ellipse in across-sectional section without a yield nose (62).
 13. A rotary motor inaccordance with claim 1, wherein the housing (2) has a cylindrical innerjacket surface differing from the circularly cylindrical shape, at whichthe outer jacket surface (13) of the piston (10) is guided androtationally fixedly supported.
 14. A rotary motor in accordance withclaim 1, wherein the housing (2) has a pressed-flat cross-section,preferably an approximately elliptical or oval cross-section.
 15. Arotary motor in accordance with claim 1, wherein the housing (2) has across-section whose outer contour differs from its inner contour.
 16. Arotary motor in accordance with claim 1, wherein the housing (2) is madeas an extruded section and/or as an extrusion molded section.
 17. Arotary motor in accordance with claim 1, wherein the housing (2) is madeas a compound housing which has a plurality of mutually connected shellsset into one another.
 18. A rotary motor in accordance with claim 17,wherein the shells are made of different materials.
 19. A rotary motorin accordance with claim 1, wherein the compound housing comprises aninner shell in engagement with the piston (10) and an outer shellforming the outer envelope of the housing.
 20. A rotary motor inaccordance with claim 19, wherein a support body, preferably of a foammaterial and/or of a cast material, which connects the outer shell tothe inner shell, is provided between the inner shell and the outershell.
 21. A rotary motor in accordance with claim 1, wherein a seal(14) is inserted into the outer jacket surface (13) of the piston (10)being in rotationally fixed engagement with the inner jacket surface ofthe housing (2).
 22. A rotary motor in accordance with claim 1, whereinthe piston (10) is supported at the housing (2) and/or at the shaft (3)by plain bearings.
 23. A rotary motor in accordance with claim 1,wherein the piston (10) is supported at the housing (2) and/or at theshaft (3) by roller bearings (32; 41).
 24. A rotary motor in accordancewith claim 1, wherein the twisted polygonal section of the shaft (3) hasa uniform pitch over its length.
 25. A rotary motor in accordance withclaim 1, wherein the twisted polygonal section of the shaft (3) has apitch changing over the length of the shaft (3).
 26. A rotary motor inaccordance with claim 1, wherein a plurality of pistons (10) are seatedon the shaft (3) in screw engagement.
 27. A rotary motor in accordancewith claim 1, wherein two pistons (10) to be moved in opposite sensesare arranged on the shaft (3) and the shaft (3) and/or the housing (2)have screw engagement sections in opposite senses.
 28. A rotary motor inaccordance with claim 1, wherein the shaft (3) is radially supported ata direction change section (49).
 29. A rotary motor in accordance withclaim 1, wherein the shaft (3) is supported at a direction changesection (49) and/or axially approximately centrally.
 30. A rotary motorin accordance with claim 1, wherein two pistons (10) or piston parts (10a, 10 b) biased axially with respect to one another are seated on theshaft (3).
 31. A rotary motor in accordance with claim 1, wherein a biasapparatus for the biasing of the two pistons (10) or piston parts (10 a,10 b) comprises a hydraulic pressure store between the two pistons (10)or piston parts (10 a, 10 b) and/or can be fed by pressure medium fromthe pressure chambers (15, 16, 17, 18) for the actuation of the piston(10).
 32. A rotary motor in accordance with claim 1, wherein the twopistons (10) or piston parts (10 a, 10 b) can be biased toward oneanother or apart from one another by a mechanical spring device (39).33. A rotary motor in accordance with claim 1, wherein the shaft (3) issupported by means of bearing covers (4) which are seated axially at endfaces at the ends of the housing (2) and close the latter.
 34. A rotarymotor in accordance with claim 1, wherein seals are provided between thebearing covers (4) and the shaft (3) for the sealing of the pressurechambers (15, 18), with the seal preferably being integrated in thebearing surface in each case at which the shaft (3) is rotatablysupported at the bearing cover (4).
 35. A rotary motor in accordancewith claim 1, wherein the shaft (3) is shaped from a substantiallycylindrical shaft blank which has a polygonal sectional cross-sectiondiffering from the circular shape, the shaft blank is twisted in itselfaround its longitudinal axis by non-cutting shaping so that its outercontour forms a polygonal section twisted in itself.
 36. A method inaccordance with 35, wherein the shaft blank is twisted in oppositesenses starting from a direction change section (49) toward oppositelydisposed sides.
 37. A method in accordance with claim 36, wherein twoshaft blanks twisted in opposite senses are rotationally fixedlyconnected to one another, preferably screwed to one another and/orwelded to one another.
 38. Use of the rotary motor in accordance withclaim 1 for the pivoting of a loading board wall of a truck.